This is a peeve of mine too, but as long as attention is paid to this problem, jQuery-laden popup login forms can be built that work automatically with password

This is a peeve of mine too, but as long as attention is paid to this problem, jQuery-laden popup login forms can be built that work automatically with password managers. There a trick to it, though, which is to put the form in a nominally 'visible' state at page load time, even if it happens to be visually obscured by other elements. Autofill will happen at page load, but will only become apparent when you make the popup div visible by bringing it to the front. Caveat: I need to re-test this with the latest version of LastPass. However, when I built a site using this method a few years ago, it did work across various password managers and different browsers, which didn't happen using the more common method of toggling the display property. The scope of this problem is more than just LastPass. Etsy's popup fails equally well with Safari's password manager. IIRC, Safari was the pickiest of the browsers about how the login box was hidden, but password autofill did work with it in the end.